Solution - Long multiplication
Step-by-step explanation
1. Rewrite the numbers from top to bottom aligned to the right
| Place value | ones | . | tenths |
| 4 | . | 2 | |
| × | 0 | . | 9 |
| . |
Ignore the decimal points and multiply as if these are whole numbers (as if each most right digit is the ones digit):
In this case we removed 2 decimal place(s). So once calculated, the result will be reduced by the factor of 100.
| Place value | hundreds | tens | ones |
| 4 | 2 | ||
| × | 9 | ||
2. Multiply the numbers using long multiplication method
Start by multiplying the ones digit (9) of the multiplier 9 by each digit of the multiplicand 42, from right to left.
Multiply the ones digit (9) of the multiplicator by the number in the ones place value:
9×2=18
Write 8 in the ones place.
Because the result is greater than 9, carry the 1 to the tens place.
| Place value | hundreds | tens | ones |
| 1 | |||
| 4 | 2 | ||
| × | 9 | ||
| 8 |
3. Add the partial products
Multiply the ones digit (9) of the multiplicator by the number in the tens place value and add the carried number (1):
9×4+1=37
Write 7 in the tens place.
Because the result is greater than 9, carry the 3 to the hundreds place.
| Place value | hundreds | tens | ones |
| 3 | 1 | ||
| 4 | 2 | ||
| × | 9 | ||
| 3 | 7 | 8 |
Because we have 2 digit(s) to the right of the decimal point in the numbers that are being multiplied, we move the decimal point 2 time(s) to the left (reducing the result by the factor of 100) to get the final result:
The solution is: 3.78
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